1. Field of the Invention
This invention pertains to metal cutting, and more particularly to apparatus for trimming metal coils.
2. Description of the Prior Art
An essential step in producing sheet metal in coils is the trimming of the coil edges as it leaves the rolling station. Various equipment has been developed to perform the trimming operation. Such equipment includes pairs of cooperating rotary trimmer blades. The trimmer blades may be in the form of cylindrical disks having flat faces and sharp corners between the disk faces and the outer diameters. For satisfactory operation and long life, the trimmer blades are made of hardened steel.
The manufacture of prior trimmer blades is somewhat inefficient. That is because the manufacturing process requires a surface grinding operation on the blade faces. The surface grinding operation is time consuming and requires the use of specialized and expensive machine tools. Further, prior manufacturing methods require grinding of the outer periphery, which necessitates the use of a second grinding machine.
In operation, the trimmer blades are placed with their faces parallel to each other. Their peripheries overlap a slight distance with minimal clearance between the overlapping faces such that the faces lie in a common plane. The blades rotate in opposite directions, and their overlapping faces form a nip through which a margin of the metal coil passes. As the coil passes through the nip, the coil is sheared along the common plane.
After extended service, the trimmer blades begin to dull. The sharp corners become rounded and eventually lose their cutting ability. At that time, the trimmer blades are removed from service and are resharpened.
Because of the hardness of the trimmer blades, resharpening prior trimmer blades presents a problem. Their faces must be ground, but many sheet steel mills which make coils do not have surface grinding equipment. Consequently, prior art dull trimmer blades must be sent to the manufacturer for resharpening, which results in undesirable shipping and handling costs. Repeated surface grinding of these blades reduces the thickness of the blade hub. Hence, spacers may be required if there is not adequate thread length on the arbor. In addition, resharpening the trimmer blades at the factory by surface grinding is a slow and expensive operation.
Thus, a need exists for improvements in the field of trimmer blades.